Why do basil leaves turn yellow and how can this be prevented or treated?

Basil leaves turn yellow due to various reasons such as overwatering, nutrient deficiencies, pests, or diseases. To prevent or treat yellowing leaves, ensure proper watering, provide adequate sunlight, use well-draining soil, fertilize appropriately, and monitor for pests or diseases. Pruning damaged leaves and promoting overall plant health can also help prevent yellowing.